Commercial transport aircraft manufacturers are under continual pressure to increase the operating efficiency of passenger and cargo aircraft. A major component of operating costs is aircraft fuel, and a major contributor to aircraft fuel consumption is aerodynamic drag. Accordingly, manufacturers have investigated a myriad of techniques for reducing aircraft drag.
One such technique includes maintaining laminar boundary layer flow over aircraft wetted surfaces, particularly the wings, because the drag associated with laminar flow is typically less than the drag associated with turbulent flow. Laminar flow control techniques typically fall into one of three categories: (a) natural laminar flow control, which relies primarily on aerodynamic shaping to maintain laminar flow, and does not require a powered device to do so, (b) active laminar flow control, which requires a powered device to maintain laminar flow, and (c) hybrid laminar flow control, which is a combination of natural laminar flow control and active laminar flow control. Natural and hybrid laminar flow control techniques have received additional attention recently because they require no power (or at least reduced power) when compared with active laminar flow control techniques.
One of the difficulties associated with achieving laminar flow via any of the foregoing techniques is the potential for degradation in laminar flow performance due to surface roughness. Surface roughness has long been known to play a role in causing transition from laminar flow to turbulent flow on swept aircraft wings. However, the cost of manufacturing a very smooth wing surface, particularly over large regions of the wing, can be prohibitive. Accordingly, there is a need for cost effective techniques for making and operating laminar flow aircraft wings.